Waste Water Treatment

Assignments Draw, label and explain each step in the wastewater treatment process.

Pollution from Sewage Sewage: Poses a threat to public health because it carries disease-causing agents (cholera bacteria, hepatitis, E. coli, coliform bacteria). Causes cultural eutrophication in surface waters. Causes an increase in BOD (biological oxygen demand) which causes a decrease in overall available oxygen

Sewage Treatment Sewage treatment means removing impurities so that the remaining waste water can be safely returned to the surface waters (river, bay, ocean) and become part of the natural water cycle again. Sewage treatment separates solids from liquids by physical processes and purifies the liquid by biological and chemical processes

Reducing Water Pollution through Sewage Treatment Raw sewage reaching a municipal sewage treatment plant typically undergoes: – Primary sewage treatment: a physical process that uses screens and a grit tank to remove large floating objects and allows settling. – Secondary sewage treatment: a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable oxygen demanding organic wastes.

Sewage Treatment Plants Facilities that clean the waste materials out of water

Reducing Water Pollution Through Sewage Treatment Advanced or tertiary sewage treatment: – Uses series of chemical and physical processes to remove specific pollutants left (especially nitrates and phosphates). Water is chlorinated to remove coloration and to kill disease-carrying bacteria and some viruses (disinfect).

Primary Treatment: mechanical process Preliminary: large objects screened 1)Removes 60% of the suspended solids and 30% of oxygen demanding wastes from sewage 2)Grease and oils removed, organic solids sent to biosolids treatment – Uses screens to filter out debris such as sticks, stones and rags – Allow suspended solids to settle out as sludge in settling tank

Primary Treatment Step 1: Dirty water is passed through a large screen to catch solid objects such as paper, rags, and bottle caps

Primary Treatment Step 2: Water is then placed in large tank where smaller particles, or sludge can sink and be filtered out. Any floating scum is scooped off surface such as oil.

Secondary Treatment biological process Aeration process (add oxygen) 1) Aerobic bacteria remove 90% of biodegradable, oxygen-demanding organic waste still left over Activated sludge process: pump sewage into large tank and mix for several hours with bacteria-rich sludge and air bubbles Then goes to sedimentation tank where microorganisms and suspended solids settle out as sludge Sludge produced is incinerated, sent to landfill or treated in biosolids facility Secondary removes only tiny fraction of radioactive isotopes and persistent organic substances such as pesticides

Secondary Treatment Step 3: The water is then sent to the aeration tanks where it is mixed with oxygen and bacteria. The bacteria feed on the waste and use the oxygen

Secondary Treatment Step 4: The water then goes to another settling tank, where chlorine is added to disinfect the water.

Secondary Treatment Step 5: The water is finally released into a water source such as a river, lake, or ocean.

Tertiary Sewage Treatment Water travel through coal filters that remove specific pollutants left in water after primary and secondary – These advanced plants cost twice as much to build and four times as much to operate. Water from primary, secondary, and advanced treatment plants is bleached and disinfected by chlorinating. Sewage Sludge (36% by weight) is applied to farmland as fertilizer for crops used for animal feed and human food. 38% is dumped into landfills;16% is incinerated; 9% is composted Growing interest in using membrane based technologies reverse osmosis, micro filtration, ultra filtration and nanofiltration

The total process Because of Clean Water Act, most U.S. cities have combined primary and secondary sewage treatment plants Before discharge, water from all three processes undergo – bleaching to remove water coloration – disinfection to kill disease-carrying bacteria (chlorination)

Technological Approach to Point source Pollution Septic Tanks: sewage from each house goes into holding tank on property – 25% of all homes Sewer lines: urban areas; waste flow through series of pipes leading to treatment center – Some cities have separate lines for sewage and storm water; some combined lines so if rains flood system, often discharges untreated sewage into surface water

Reducing Water Pollution through Sewage Treatment Septic tanks and various levels of sewage treatment can reduce point-source water pollution Septic Systems require suitable soils and maintenance

Where does the Water Come From In North Carolina more than ½ the people get water from groundwater Most comes from aquifers Most important from aquifers in coastal plains

Where Water Comes From More than half of the people living in North Carolina depend on groundwater for their water supply. Groundwater in North Carolina is stored in aquifers that are located in the subsurface throughout the state.

Where the Water Goes Water in Agriculture Most of the water that is lost during farming is lost through evaporation and runoff. Water in Industry About 19% of water used in the world is used for industrial purposes, such as manufacturing goods.

Where the Water Goes, continued Conserving Water at Home You can help conserve water by taking shorter showers and by turning the water off while brushing your teeth. This graph shows how water is used in the home.